docs: def pickle(self) -> None:
          """ Pickles the Corpus object in a file in tgt_dir. """
  
          pickle_path = self.tgt_dir / "corpus.p"
          logger.debug("pickling %r object and saving it to path %s", self, pickle_path)
          with pickle_path.open("wb") as f:
              pickle.dump(self, f)